a === b -> identical(a, b)

tests/utils/dummy_compiler_test.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 // Smoke test of the dart2js compiler API.
 
 import '../../sdk/lib/_internal/compiler/compiler.dart';
 import 'dart:uri';
 
 Future<String> provider(Uri uri) {
@@ skipping 29 matching lines @@
       source = "#library('lib');";
     }
   } else {
    throw "unexpected URI $uri";
   }
   completer.complete(source);
   return completer.future;
 }
 
 void handler(Uri uri, int begin, int end, String message, Diagnostic kind) {
-  if (uri === null) {
+  if (uri == null) {
     print('$kind: $message');
   } else {
     print('$uri:$begin:$end: $kind: $message');
   }
 }
 
 main() {
   String code = compile(new Uri.fromComponents(scheme: 'main'),
                         new Uri.fromComponents(scheme: 'lib', path: '/'),
                         new Uri.fromComponents(scheme: 'package', path: '/'),
                         provider, handler).value;
-  if (code === null) {
+  if (code == null) {
     throw 'Compilation failed';
   }
 }